The present invention relates to apparatus for applying fluid droplets to a writing surface, and more particularly to such a system which prevents the liquid in the discharge channel from becoming dry during standby periods to eliminate the problem of clogging of the discharge channel.
The liquid applying head comprises a liquid chamber for containing liquid therein, a liquid discharge channel and an electromechanical transducer for generating pressure rises in the liquid chamber to expel the liquid through the discharge channel into the atmosphere onto a writing surface which is a sheet of paper rolled on a rotating drum. Since the ink liquid in the forward end of the discharge channel is always exposed to the air, it tends to lose its liquidity with time and retard the ejection of liquid to the writing surface.
U.S. Pat. No. 4,106,032 discloses a liquid applying apparatus in which a stream of moisture laden air is simultaneously ejected along the passage of the discharged liquid through an air nozzle coaxially disposed with the liquid nozzle to accelerate the liquid to the writing surface and to maintain the liquidity of the ink at the exit end of the discharge channel at all times. However, this prior art apparatus has disadvantages in that (1) the moistened air stream tends to blur the image produced on recording paper, (2) because of the moisture the recording paper tends to attach to the rotating drum, making it difficult to remove the paper therefrom, and (3) since the humidified air is supplied only when the apparatus is operating, the liquid in the ejection nozzle tends to dry during the time when the apparatus is in standby mode.